The Belgian, who is set to miss the remainder of the season and the FIFA World Cup in Brazil, was forced off on a stretcher during his side's 1-1 Bundesliga draw with Hertha Berlin on Sunday after colliding with opposition striker Adrian Ramos.
The club confirmed the 21-year-old had suffered a broken tibia on their Twitter account on Sunday, and have now offered an update on his condition.
"According to the doctors, the almost two-hour long procedure went without complications," read a statement on the club's website on Monday. "It is expected on Wednesday Casteels will leave the Berlin clinic and can start after having first light rehab exercises in the TSG training centre in Zuzenhausen."
Former Genk player Casteels has been at Hoffenheim since 2011 and has represented Belgium at Under-21 level.
He is yet to make a senior appearance for the national side, but was expected to go to the World Cup as third-choice goalkeeper behind Simon Mignolet and Thibaut Courtois.
Casteels is the second Belgian international to have suffered a serious injury in quick succession, following Christian Benteke's ruptured Achilles tendon last week.
